Once upon a time there was a world of tragic princes who had been transformed into small amphibians, beautiful princesses who were temporarily languishing in a life of drudgery, unprepossessing trolls with rights-of-way issues, and a variety of woodland wildlife with surprisingly philanthropic attributes.

All this week the Guardian is giving away booklets of our best-loved fairytales (that can also of course be read on the web), with their contemporary resonances discussed by the modern writers who have selected the stories for publication. But the deeper you venture into the dark woods of these fairytales, the more you have to wonder – are these stories really for kids?

When our son was very young I embarked on a mission to expand his literary horizons and purchased a copy of the fairy stories of the Brothers Grimm to read to him each night. He was little more than a babe in arms at the time, and the whole enterprise was really a tool to lull him into a peaceful sleep. He often dozed off within a couple of pages of each story, but I would continue to read aloud in hushed tones, largely for my own edification.

If he slept soundly, though, I went to bed more troubled. The Disneyfication of fairy stories over the past 70-odd years since Uncle Walt released his animated take on Snow White and the Seven Dwarfs has put into most people's minds a primary-coloured world of beautiful people facing dastardly villains and apparently insurmountable obstacles on their path to a life of happiness alongside Mr or Ms (or, more likely, HRH) Right; a world where good always triumphs and there's no better relationship than one built upon the size of a kingdom. A world, largely, for children. But the picture painted by the Grimms was of a vast, dark, world-encompassing forest in which still darker deeds were committed – and went unpunished.

Lopping off heads with axes was de rigueur; the story of The Robber Bridegroom, to cite one particularly bloody example, contained a horrifying passage in which the robbers "dragged with them another young girl. They were drunk, and paid no heed to her screams and lamentations. They gave her wine to drink, three glasses full, one glass of white wine, one glass of red, and a glass of yellow, and with this her heart burst in twain. Thereupon they tore off her delicate raiment, laid her on a table, cut her beautiful body in pieces and strewed salt thereon." But all this X-rated brutality isn't as out of place as it might at first appear. The folk tales that have, over the years, become sanitised and cutesy, originally started life as stories for grown-ups.

The godfather of modern fantasy, JRR Tolkien, wrote an essay in 1938 entitled On Fairy Stories to give as a lecture at St Andrew's University. As the world rumbled towards global conflict, Tolkien turned inward, musing: "The association of children and fairy stories is an accident of our domestic history. Fairy stories have in the modern lettered world been relegated to the 'nursery', as shabby or old-fashioned furniture is relegated to the playroom, primarily because the adults do not want it, and do not mind if it is misused."

The author Neil Gaiman, writing for the Guardian in 2007 on the occasion of the release of the movie version of his "fairytale for adults", Stardust, said: "Children listened to them and enjoyed them, but children were not the primary audience, no more than they were the intended audience of Beowulf, or The Odyssey … Fairytales became unfashionable for adults before children discovered them, though. Wilhelm and Jacob Grimm, to pick two writers who had a lot to do with the matter, did not set out to collect the stories that bear their name in order to entertain children. They were primarily collectors and philologists, who assembled their tales as part of a life's work that included massive volumes such as German Legends, German Grammar and Ancient German Law. And they were surprised when the adults who bought their collections of fairytales to read to their children began to complain about the adult nature of the content."

Modern writers have attempted to return fairy tales to their adult roots more than once. Angela Carter's collection The Bloody Chamber upped the sex and violence content in tales based on Puss in Boots, Beauty and the Beast and Bluebeard. Self-proclaimed "mythographer" Marina Warner teaches a course in fairy tales at the University of Essex and has published several volumes of fairy stories for adults. The latest entry into the genre, published this month, is In Sleeping Beauty's Bed, a book of "erotic fairy tales" by Mitzi Szereto, said by one reviewer to "guaranteed to unleash the wolf within and leave Red Riding Hood blushing".

It would be a shame, though, if fairy stories – notwithstanding their origins as tales for grown-ups – were completely removed, in Tolkien's words, from the playroom. Sanitised and Disneyfied many modern versions may be, and the expectations of how life pans out they engender, especially among young girls, might not be completely desirable, but they do help to instil in children a sense of wonder that is vital for navigating the often dark and dense forest of adult life.